Heparan sulfate (HS) and chondroitin sulfate (CS) glycosaminoglycans play important roles in many physiological and pathological events, such as cell division, inflammation, neuronal development, and cancer metastasis. Naturally existing HS and CS display a diverse range of sulfation patterns. While this structural diversity bestows HS and CS with the ability to interact with many proteins, it greatly hinders the ability to decipher their structure-function relationships. In order to dramatically advance an understanding of the biological functions of glycosaminoglycans, it is critical to access large, structurally diverse libraries of HS and CS oligosaccharides bearing well-defined sulfation sequences. To date, synthetic methodologies toward HS and CS are mostly target oriented, resulting in only small sets of oligosaccharides. Furthermore, it remains difficult to prepare HS and CS sequences longer than a dodecasaccharide. To address these challenges, three research groups with strong, complementary expertise in HS and CS synthesis and biology have joined forces to accomplish the following aims. In Aim 1, new synthetic strategies are proposed to accelerate the synthesis of HS oligosaccharides. Methodologies will be developed to prepare the first comprehensive library of 256 HS tetrasaccharides representing all of the possible 2-O, 6-O and N sulfation motifs, along with a library of structurally diverse 3-O sulfated tetrasaccharides and HS hexasaccharides. In Aim 2, we propose new efficient, cost-effective routes to access the first comprehensive library of CS tetrasaccharides bearing all of the possible mammalian sulfation sequences. In Aim 3, HS/CS oligosaccharide-based polymers and head-to-tail multimers will be prepared to enable access to structures containing homogeneously sulfated glycans with sizes approaching natural polysaccharides. These mimetics will possess similar domain structures and multivalent properties found in naturally existing CS and HS polysaccharides. In Aim 4, we will validate the hypothesis that our molecules can recapitulate the biological functions of HS and CS polysaccharides using well-established assays, including anticoagulation, neuronal growth, and protein-binding assays. Furthermore, we will explore the potential for these molecules to selectively target a clinically important family of proteins, the fibroblast growth factors. Together, this project will provide faster, more affordable syntheses of HS and CS, greatly expand the chemical space currently accessible by synthesis, enable the first direct, in-depth comparisons between HS and CS, and provide novel agents to control the activities of these biomedically important molecules.